Electrosurgical tool systems are used to cut tissue, shape tissue, coagulate tissue and ablate tissue at surgical sites to which the tools are applied. Generally, an electrosurgical tool system includes an electrode with at least one electrically active tip. An electrode that has a single active tip is referred to as monopolar. An electrode with at least two active tips is typically referred to as bipolar. A control console, also part of the system, supplies an RF signal to the electrode. Often this signal is between 50 KHz and 10 MHz. The RF signal is applied to the active tip(s). If the system includes the monopolar electrode, a second dispersive electrode, is placed in contact with the patient to serve as a return path for the RF signal. If the system includes a bipolar electrode, the active tips alternate as active and return poles during the RF cycle.
One medical specialty in which electrosurgical tools are used with increasing frequency is pain management. Pain is felt as a consequence of first, a stimulus being applied to a first nerve. Then, a signal representative of the pain is transmitted from the first nerve through the other nerves in the neural network to the brain. An individual can suffer chronic pain if the biological conditions are such that the first nerve latches into a condition in which it continually transmits the pain signal through the neural network to the brain.
In a pain management process, an electrosurgical tool is used to remove either the initial pain transmitting nerve or one of the associated downstream nerves from the neural network. This disconnection stops the flow of pain messages to the brain. Medically, the process of removing the nerve from the nerve network is called denervation.
In a denervation process, the RF energy emitted by the electrode is applied to the nerve. The nerve absorbs this energy and, as a consequence, is heated to the level at which it ablates.
Presently, the common practice is to use a monopolar electrode assembly to apply the RF energy to the nerve that is to be subjected to ablation. The electrode assembly has two separate components, a cannula and a supply electrode. The cannula is a tube like structure. At the distal end tip, the end positioned at the surgical site, there is an active electrode tip. The supply electrode is inserted in the bore that extends through the cannula. Fitted to the supply electrode is a temperature sensitive transducer.
In the denervation procedure, the surface location above the nerve to be ablated is first anesthesized. The cannula is then inserted through the skin and directed toward the nerve. The supply electrode is fitted to the cannula. A low powered signal is then applied to the supply electrode. This electrode assembly is thus used as a supply electrode to precisely identify the position of the nerve. Once the position of the nerve is determined, the supply electrode is withdrawn from the cannula. An anesthesia is introduced through the cannula to the procedure site in order to numb the tissue at the site. The supply electrode is then reinserted into the cannula. At this time, a higher powered signal is applied through the supply electrode to the active tip integral with the cannula. These high powered RF signals are what are absorbed by and cause the ablation of the nerve.
During the ablation process, the transducer provides an indication of the temperature of the tissue being subjected to ablation. The medical personnel use this information to regulate the application of power to the electrode assembly.
There are many situations however wherein it is desirable to use a bipolar electrode in order to apply RF energy in order to perform the denervation procedure. This is because, the energy flow when using this type of electrode is essentially between the two active tips. Thus the energy flow at the surgical site is more directed than when a monopolar electrode with a large area external ground pad is employed. As a consequence of this more directed energy flow, more energy is applied in a shorter amount of time to the tissue, the nerve, to be ablated. Inversely, less energy is absorbed by nearby tissue that should be subjected to ablation. Thus, using a bipolar electrode to perform the ablation process would further result in a denervation process that is less likely to harm surrounding tissue.
However, to date, there have been obstacles to using bipolar electrodes for denervation procedures. This is because it has proven difficult to provide bipolar electrode assemblies that are relatively small in size. Small diameter electrodes are needed in order to ensure the precision application of the RF energy to the nerve to be ablated. Also, it is desirable to design the electrode so that when inserted into the patient, the skin is exposed to minimal trauma. Large diameter electrodes, with sections having different stepped outer diameters, could potentially cause aggravated trauma to the skin and underlying tissue during the insertion process.
One could provide a bipolar electrode assembly that is solid. Such an assembly would be small in diameter. However, such an assembly would not provide the through bore desirable for introducing anesthesia or agents to the surgical site.
Further different sized and shaped electrode assemblies are available to surgeons. These different sizes and shapes facilitate the position of their distal end tips at the locations where they are to be used to perform treatment. Sometimes the cannulae and supply electrodes appear to match when, in fact, they do not. This requires the medical personnel to take additional time to ensure that the proper cannula and supply electrode pair are assembled together to form the electrode assembly.